Talk:Validity vs. soundness

I rewrote this to correct an error and expand the topic a bit. The original content included the following:

I either own a bicycle or a car.

I don't own a bicycle.

Therefore, I own a car.

The premises can both be true, that is, it's possible for me to own a car but not a bicycle. However, it's not necessarily true that, just because I don't own a bicycle I must own a car. Thus, this argument is valid but not sound.

This argument is actually valid and sound as the first premise declares a direct dichotomy and the second premise eliminates one prong.

In any case, the current article has a link or two that will need to be expanded. I'll try to add the syllogism page and include the named forms and an explanation of why those forms are valid, as opposed to others. -- Sans Deity 20:34, 30 August 2006 (MST)

Wrong! It's valid because the conclusion is proven by the premises. Soundness has only to do with the truth of the premises. For example:

Sadam Hussein either has weapons of mass destruction or he has a cheese cake factory.

Sadam Hussein has no weapons of mass destruction.

Ergo: Sadam has a cheese cake factory.

This conclusion or "ergo" is a direct result of the premises. If Sadam as a result doesn't have a Cheese Cake factory then the argument is invalid. However, it is true that the truth value of the premises are independent of validity. It could be true that Sadam Hussein had neither,making it false and unsound, but if the argument is presented in the above format it will still be valid. --carlos (2010-07-01)

Not knowing the truth of a premise does not automatically make the argument unsound, though. You can easily show that it's false to state "all people have either a bicycle or a car", but it isn't necessarily false for a person to state "I have either a bicycle or a car." You would need to verify the conclusion to know if that premise is true or false.

That example demonstrates why similar logical argument can be so readily accepted by creationists. The premises are written in such a way that they would be true if the conclusion were true... and the conclusion has been accepted a priori.